Perhaps check references to determine if either candidate was able to work well in the type of environment you provide.
For example - the nice person may be lazy, or the abrasive person may productive and helpful.
It's been my experience that contacting the candidates references will flush that information out. Even in this age of litigation - I've always been able to get an answer to "Please rate on a scale of 1 to 10"
We've avoided some people that interviewed well and had great skills but were horrible human beings - and we've picked up some people that are hard workers that are willing to learn that didn't interview well.